Vehicle seats generally include a reclining device that is capable of adjusting the tilt angle of a seat back relative to a seat cushion.
The reclining device disclosed in Patent Document 1, for example, includes a first bracket (gear plate) having internal teeth on an annular inner circumference, pawls (lock gears) each having external teeth that are engageable with and disengageable from the internal teeth, and a second bracket (base plate) having guide portions that retain the pawls to be movable in a radial direction. The second bracket is rotational relative to the first bracket. The reclining device further includes a cam mechanism, which has a cam body located radially inward of the pawls. The cam mechanism is configured to move the pawls in the radial direction according to rotation of the cam body so that the external teeth of the pawls engage with and disengage from the internal teeth of the first bracket. One of the first bracket and the second bracket is secured to the seat cushion, and the other is secured to the seat back.
When the pawls move radially outward and the external teeth mesh with the internal teeth of the first bracket, relative rotation between the first bracket and the second bracket is restricted (locked state). When the pawls move radially inward and the external teeth disengage from the internal teeth of the first bracket, relative rotation between the first bracket and the second bracket is permitted (unlocked state). The tilt angle of the seat back can be adjusted in this unlocked state.
However, when load is applied to the seat back such as when an occupant leans against the seat back, pressure that pushes the internal teeth of the first bracket and the external teeth of the pawls toward each other is applied. If the locked state is cancelled in this state, unlocking may fail to be smoothly performed such as a case where the locked state is suddenly cancelled or noise is generated, and operational sensation of unlocking may be undesirably degraded.
To address this problem, for example, Patent Document 2 discloses a structure that improves ease of separation of the external teeth from the internal teeth by further adding an inclination angle (draft angle) to a pressure angle of an end tooth located on one circumferential end or on each of both circumferential ends among the external teeth of each pawl.
If, however, a draft angle is added to the pressure angle, the size of the external teeth is reduced. Meshing strength between the internal teeth and the external teeth, that is, locking strength is consequently reduced, and feel of rigidity of the seat back may be undesirably reduced.
Based on that fact, Patent Document 1 discloses a structure in which, in each of the pawls, the pitch circle radius formed by at least one external tooth including the end tooth located on a first circumferential end is set smaller than the pitch circle radius of the internal teeth, and the pitch circle center formed by at least one external tooth including the end tooth is decentered with respect to the pitch circle center of the internal teeth toward the internal teeth and toward the end tooth located on a second circumferential end.
With this configuration, the tooth tip of at least one external tooth including the end tooth located on the first circumferential end tilts toward the first circumferential end. The ease of separation of the external teeth from the internal teeth is thus improved while maintaining the size of the external teeth and ensuring the required meshing strength.